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    Re: Single LOP is enough?
    From: Bill Lionheart
    Date: 2020 Sep 15, 22:01 +0100

    Of course if you could measure the azimuth accurately (eg on land) as
    well as the altitude you would be on (one of) the intersection(s) of
    the isoazimuth and the circle of position. Summary of discussion we
    had here earlier this year (and the paper I have not finished writing)
    "Isoazmuth curves can be surprisingly strange".
    
    Bill
    
    On Tue, 15 Sep 2020 at 21:17, Frank Reed  wrote:
    >
    > The key detail here: that azimuth that you see in the intercept method is 
    calculated from your input! It cannot help you fix your position all by 
    itself because it can have any value, dependent on the DR or AP or other 
    position that you feed into the calculation process. We don't have any means 
    of observing azimuths with great accuracy, but if we did, we could use them 
    for celestial position fixes.
    >
    > Let's imagine a super-compass enabling us to observe the azimuth of a star 
    to the nearest tenth of a minute of arc. Typical real compasses can get you 
    the azimuth to the nearest degree under good conditions and often worse. So 
    this super-compass would be on the order of 500 to 1000 times better at 
    measuring azimuths than anything we have today.
    >
    > Now observe the Sun with your (common) sextant and also your super-compass. 
    You get an altitude of, let's say, 60°15.5' (after applying altitude 
    corrections), and from your super-compass you get an azimuth of perhaps 
    175°12.0'. Then you look up the Sun's astronomical data, and you select and 
    arbitrary position near where you think you are to use as an "AP". From that 
    AP you calculate that the Moon's altitude should be 60°10.0' and it's azimuth 
    should be 175°09.5'. That tells us that our vessel is 5.5 nautical miles 
    towards the Sun, and it is also some miles (there's a little math involved) 
    to the left of the arbitrary AP (to the left when facing the Sun). With those 
    two observed pieces of information, we could fix our position. But there are 
    no super-sextants, at least not in commercial production.
    >
    > There's a general principle at work here. We want two numbers out of our 
    navigation process: latitude and longitude (or some equivalent x, y 
    coordinates). To get two quantities out, we need to feed two observed 
    quantities in. In normal celestial navigation, we observe two altitudes to 
    get latitude and longitude. With super-compass celestial navigation, we could 
    observe one altitude and one azimuth at the same time to get latitude and 
    longitude. Two in, two out.
    >
    > Frank Reed
    > ReedNavigation.com
    >
    > View and reply to this message
    

       
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